High-pressure die



J. F. H. CUSTERS ET! AL Nov. 6, 1962 HIGH-PRESSURE DIE 3 Sheets-Sheet l Filed Oct. 51, 1960 w W 0 H M h w Him m M ww i ch z 74 fl pf 4 y M M 2 E m% wflria 3 3/ a a Q Nov. 6, 1962 J. F. H. CUSTERS EI'AL 3,

HIGH-PRESSURE DIE 3 Sheets-Sheet 2 Filed Oct. 51, 1960 Jim men 4/ 54-71004 fiznse 77 #425 0;

8r QM Ar rx Nov. 6, 1962 STERS EI'AL United tates The object of the present invention is to provide a die capable of exerting pressures on material enclosed within its pressure chamber of the order of say 50,000 atmospheres and above. While it is not excluded that the die be used to compress the material in the cold, the purpose for which the die of the invention has been evolved is to compress the charge and heat to it elevated temperature simultaneously, so that the object of the invention is also to provide a die which can successfully be applied to this end.

The production of dies which are capable of imposing on the material charged into them high pressures of the order of 50,000 atmospheres and above presents no great technical difiiculties. Indeed, in laboratory equipment dies have been made in which pressures up to 80,000 atmospheres have been achieved. Similarly, there is no difficulty in bringing material to elevated temperature, say up to 1800 C. and this can readily be achieved while the material is kept under moderate pressure. Where, however, grave difficulties do arise is when material is to be heated to temperatures of this order and simultaneously maintained under high pressure of the order of say 80,000 atmospheres.

In its broadest aspect the die of the invention consists in a dished and cavitied core, an anvil having a frusto-conical or -conoidal peak, that is accommodated within the dishing of the core, is separated from the core by empty space and occludes the adjacent end of the cavity in the core, means occluding the other end of the cavity, and a body within the cavity hollowed to form a pressure chamber made of a refractory material characterized by low compressive strength and high coefiicient of friction relatively to the surfaces of the anvils and the core in contact with the body.

In the preferred form, the die has two peaked anvils accommodated within a core dished at opposite faces.

The core may have a central insert of expandable material characterized by high resistance to compressive forces; or it may be integral.

The detailed construction of the preferred form of the die will best be understood if it be described with reference to the accompanying drawings. In these drawings,

FIGURE 1 is a vertical section,

FIGURE 2 is a section of the pressure zone on an enlarged scale,

FIGURE 3 is a section through the assembly within the pressure chamber,

FIGURE 4 is a modification of FIGURE 3,

FIGURE 5 is a detail view of another form of charge,

FIGURE 6 is a detail view of a modification of the arrangement of FIGURE 5, and

FIGURE 7 is a detail view of a modified core.

In the drawings, the core is a ring 10 which is cylindrical and dished on both its faces. The anvils i2, 14 are also cylindrical and are formed with opposed frustoconical or -conoidal peaks 16, 18 that are accommodated within the depressions in the ring 10 that separates the anvils, so that the cavity of the ring is closed off by the flattened ends of the peaks to define a pressure chamber 20. The corners of the ring directed towards the chamber "atent 20 are radiused, while the corners 22 of the peaks are sharp.

T he included angle of the peaks may be somewhat less than the angularity of the dishing of the ring, so that the opposed faces 24, 26 and 28, 30 of the ring and the anvils diverge outwardly at an angle of the order of say two degrees; or the opposed faces may be parallel.

The ring and the anvils are made of refractory material such as cemented hard-metal. The properties of the hardmetal are selected to give maximum compressive strength to the anvils and good compressive strength allied with high tensile resistance to the ring. For the anvils a fine to medium grained tungsten carbide with a low content of cobalt may be used. For the ring, a medium to coarse grained tungsten carbide with medium cobalt content is suitable.

The ring 10 is buttressed against bursting forces by a ring or rings of high-tensile steel. In the drawings, three rings, 32, '34, 36 are shown. These are shrunk or forcedfitted onto the ring 10. The anvils are buttressed each by a ring 38 or 40 of high tensile steel, also shrunk or forcefitted on to the anvils.

If it be required that the die be liquid-cooled, then there are additional rings 42, 44, 46 around the two anvils and the ring 10 respectively. Between the ring 10 and each anvil there are located two rubber or rubber-like toroidal rings 48, 50; 52, 54 that provide between them annular spaces '56, 58. Each pair of toroidal rings 48, 50; 52, 54 may be mounted on a thin annular plate 60, 62. to assist in locating the toroidal rings within the assembly.

Fluid is injected into the spaces 56, 58 through doglegged ducts 64, 66 in the rings 42, 44, and withdrawn through similar ducts 68, 70 diametrally opposed to the ducts 64, 66.

The assembly is held together gravitationally with the ring 10 and its surrounding supporting rings spaced from the anvils and their supporting rings (and with the opposed flat, transverse faces 42, 44, and 46, 48 parallel) by the toroidal rings 48, 50, 52, 54-. If the die need not be liquid cooled, only one toroidal ring, to act as a spacer, will be necessary between the ring 10 and each anvil. In this case the outer rings 42, 44, '46 are unnecessary.

In a modified form of core (FIGURE 7) the central part is constituted by an inserted formation 72 of refractory material such as that sold under the trademark Diamonite. The material must be characterized by high resistance to compressive forces. The advantage of this construction is that after use the insert, which will inevitably sufier damage, can be removed and replaced by a fresh insert. The outer part of the core is little likely to suffer serious damage, at least during several uses, and can therefore be reused, thereby economizing on cost.

In the operation of the die, the pressure chamber 20 is filled with a soft, compressible, porous, thermally and electrically insulating body 7 4, possessing low compressive strength and high frictional properties, and hollowed at 76 to receive the charge 77 (FIGURE 2). A suitable material is the natural stone known as pyrophyllite or wonderstoue. The quantity of this material is specific and highly critical and small variations in this quantity give rise to different pressures in the chamber 20 with respect to a given load between the anvils 12, 14. The initial shape of the body has been shown to affect the recorded pressure with relation to load only slightly and many shapes are possible to suit particular circumstances. A cylinder with an indented periphery 78 has been found completely satisfactory.

In operation the assembly, with a charge within the pressure chamber 20, is placed between the platens of a press and load is exerted through the anvils 12, 14 on to the charge in the chamber 20. Accurate alignment of the anvil and ring 10 and its supporting rings is necessary. Circumferential alignment may be obtained by the use of a straight-edge along the periphery of the assembly, or by a clamp or flexible belt embracing the whole assembly. Horizontal parallelism is looked after by the rings 48, 50; 52, 54.

On applying pressure, the body 74 is compressed (FIGURE 2), and as the pressure increases the material tends to flow into the gaps 80, 82. between the anvils and the die ring 10. As the pressure further increases, these gaps are reduced more and more by the inward movement of the anvil faces in consequence of which the body 74 and the charge in the chamber 20 become compressed more and more. The outward flow of material through the gaps 80, 82 in inhibited by friction on the die and anvil faces. The conformation of each gap 80, 82 is such that the gap progressively narrows in the outward direction, towards the throats 84, 86, which apart from the closing movement of the die, itself inhibits extrusion of the material of the body into the gaps S0, 32.

Thus, the body 74 itself provides a barrier that is sufficient to contain the mounting pressures without the necessity for washers, seals or gaskets between the adjacent surfaces of the core and the anvils.

Further assistance may be given by coating the operative faces of the anvil and the die with a high friction abrasive material such as jewellers rouge. Also the material of the body 74 may be impregnated with a suspension of rouge to increase the friction.

By suitable design of the shape of the anvils 12, 14 and the die ring 10 a flow of the material of the body 74 may be obtained which is compatible with the maintainiug of a particular internal pressure within the pressure chamber. With the particular die configuration shown in FIGURES 1 and 2 pressures of 70,000 atmospheres may be maintained by extrusion of material into a gap of about 0.020" by 0.75" mean diameter.

So much for the production of pressure within the pressure chamber 20. The matter of heating will now be considered.

Heat is imparted to the charge within the pressure chamber by electrical current flow through a resistance element.

It is here necessary to consider the nature of the charge. If it be an electrical conductor, as it is assumed to be in FIGURES 2, 5 and 6, then the charge is itself the resistance element. Electrical current is fed along a path comprising the anvils 12, 14 and the charge. In FIGURES 2, 5 and 6, the path includes also two steel rings 88, 90 interposed between the anvils and the charge 77 and nonconductive plugs 92, 94 within the cavities of the rings 88, 90. The purpose of these rings is to prevent direct contact between the charge and the faces of the anvils, to prevent damage to them by the compressed and heated charge. The plugs 92, 94 may be of pyrophyllite.

In FIGURE 6, the rings 88, 90 are formed with lateral flanges 96, against which the anvils press.

If, on the contrary, the charge be a non-conductor or a poor conductor of electricity, as is contemplated in FIGURES 3 and 4, then the circuit must be completed by a resistance element other than the charge In FIG- URE 3 this element is shown as a tube 100. It is located within the cavity of the body '74. The most suitable materials for the tube 100 are tungsten, molybdenum or graphite but other metals or electrically conducting non-metals may be used. The ends of the heating tube 100 are sealed by electrically conducting pads 102 making good electrical contact with the anvil faces and giving a relatively low resistance and therefore low heat dissipation at the anvil surfaces. The pads 102 may be of the same material as the tube 100 and graphite is generall preferred for both because of its convenience for machining to shape. The faces of the anvils may be covered with metal shims 104- to improve electrical contact and to prevent diflfusion of the material of the heating tube 100 and end pads 102 into the refractory carbide of the anvils, thus impairing their mechanical properties. This has been found to be particularly important wherea graphite heating tube and end pads are used.

Inside the conducting pads 102 may be fitted insulating pads 106 either for the purpose of inhibiting axial heat flow which would mechanically weaken the anvil faces, or for the purpose of shielding the charge from the electric current. Also an inner tube 108 of electrically insulating material may be used. Both the pads 106 and the tube 103 serve the additional purpose of separating the charge 77 in the pressure chamber 20 defined by the pads 106 and the tube 108 from the material of the heating tube and end pads 102 in cases where it would react chemically with them or diffuse through them. Suitable materials for the pads 106 and the tube 108 are refractory oxides such as alumina, Zirconia and silica in fused or crystalline form or mineral insulators such as wonderstone.

The heating current ispased through the anvils 12 and 14 via the pads 102 and the tube 100. The resistance of the tube 100 is much greater than that of the anvils and other parts of the electrical path, causing the major part of the heat to be generated in the pressure chamber 20.

Where an internal axial temperature gradient is required, this may be procured by using a heating tube which has a continuously or discontinuously varying cross-sectional area.

The heating tube 100 may be replaced by one or more rods 110, as shown in FIGURE 4, which function in the same way as the tube and may be of the same material.

As a general comment, it may be said that the body 74 could consist in an outer part of high-friction material to minimize extrusion into the gaps between the anvils and the core, and an inner part of material incapable of supporting high shear stress. This could assist in minimizing pressure gradients within the charge.

In the case of a conductive or a non-conductive charge, alternating or direct current may be used. The latter is essential where electro-chemical or electrolysis effects are required in the pressure chamber 20.

Given an assembly in which the body 74 is of the order of 12mm. in diameter, the apparatus described has been found to be capable of generating pressures within the pressure chamber of the order of 80,000 atmospheres, while the charge is subjected to temperatures of the order of 2000 C.

We claim:

1. A high pressure dieconsisting in an annular core dished on opposite faces, two anvils straddling the core each having a frusto-conical or -conical peak that is accommodated within the dishings of the core and is separated from the core by empty space; a body within the cavity hollowed to form a pressure chamber, made of a refractory material characterized by low compressive strength and high coefficient of friction relatively to the surfaces of the anvils and the core in contact with the body, buttressing rings surrounding the anvils and the core, structure defining enclosed spaces between the buttressing rings of the anvils and the buttressing ring of the core, and means to flow cooling fluid through the spaces.

2. The die of claim 1 in which the structure consists in spaced resiliently flexible rings between the butt-ressing rings of each anvil and the core; and including ducts in the butressing rings to lead cooling fluid into and out of the spaces.

References Cited in the file of this patent UNITED STATES PATENTS 2,941,241 Strong June 21, 1960 2,941,248 Hall June 21, 1960 2,941,252 Bovenkerk June 21, 1960 2,947,034 Wentorf Aug. 2, 1960 

